Rain almost invariably
accompanies the discharge, and the roof and sides of the house being wet,
they form a more or less perfect channel of escape should a flash strike
the building.--_Knowledge._
* * * * *
RESEARCHES ON MAGNETISM.
By M. DUTER.
If we place a thin plate of steel in a uniform magnetic field, so that the
lines of force of the field may be normal to the surface of the plate, we
have a very flat magnet, the two faces of which are the two polar
surfaces. The magnetic distribution thus obtained seems to disappear when
the plate is no longer in the field. The following experiments show that
this disappearance is not complete. I made use of plates of tempered steel
of 1 millimeter in thickness, and varying in diameter from 0.040 to 0.005
meter. With these plates I formed cylindrical batteries. In some of these
batteries the plates are directly in contact, and in others they were
separated by leaves of pasteboard, the thickness of which varied from that
of the thinnest paper to 0.001 meter. The batteries were placed in the
central portion of a very powerful magnetic field, and after they have
been taken out they formed perfectly regular permanent magnets. The
supporting power of these magnets was the greater the nearer its
constituent plates were to each other.
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